METAMORPHOSIS IN

AMPHIBIANS

BY :- IQRA ASLAM

Bs zoology 5th

METAMORPHOSIS

the process of transformation

immature adult form two or more distinct stages.

In an insect or amphibian

AMPHIBIAN METAMORPHOSIS

amphi ("double") and bios ("life")

aquatic terrestrial existence

urodeles (salamanders) resorption of the tail fin

destruction of the external gills

skin structure

continue

 Morphological changes

1. GROWTH OF NEW STRUCTURES

2.  CELL DEATH

3.  REMODELING

4. BIOCHEMICAL RESPECIFICATION

Conti…..1.GROWTH OF NEW STRUCTURES limbs emerge

nictitating membranes and eyelids

Lateral eyes front eyes

New neurons spinal cord

Ephrin B cause ipsilateral

Eye migration and associated neuronal changes during metamorphosis of the Xenopus laevis tadpole

2. CELL DEATH the paddle-like tail Recent evidence , Apoptosis …….. caspase-9 Phagocytosis ……. Proteases

Gills

red blood cells Shape of cells & hemoglobin

3. REMODELING larval intestine ….. shorter

Schrieber experiment

metalloproteinase stromelysin-3

Conti…….

optic nerve pathway

motor neurons , tadpole jaw

lateral line system degenerates

ear differenciations …a brief period of deafness

SKULL

tadpole skull is primarily neural crest-derived cartilage……..

adult skull is primarily neural crest-derived bone

Changes in the Xenopus skull during metamorphosis.

4.BIOCHEMICAL RESPECIFICATION Liver

synthesize the enzymes Ammonotelic……. ureotelic

Hormonal control

1912 by Gudernatsch fed powdered horse thyroid glands

Allen (1916 destroyed the thyroid

threshold modellow concentration ……..development of limbsincreasing amounts ….. resorption of the tail

Metabolism of (T4) and (T3).

Hormone receptor

(TRa)………….. all tissues , before thyroid gland

(TRB)…………. activated by thyroid hormones. 

Stages of metamorphosis1.premetamorphosis CRH….. (TSH), …..T4…… low amounts of T3.

High levels of deiodinase II before secretion of t4….T3

limb rudiments

Metamorphic climax stage concentration of T4 rises

TRB levels peak inside the cells

deiodinase II is expressed as tail resorption, gill resorption, and intestinal remodeling

Regionally specific developmental programs

Thank you